Systems and methods for coding transform coefficient level values

ABSTRACT

This disclosure relates to video coding and more particularly to techniques for performing entropy coding. According to an aspect of an invention, a parity level flag specifying a parity of a transform coefficient level at a scanning position is decoded if a value of a second absolute level greater flag is equal to a first value.

CROSS REFERENCE

This Nonprovisional application claims priority under 35 U.S.C. § 119 on provisional Application No. 62/729,942 on Sep. 11, 2018, No. 62/732,454 on Sep. 17, 2018, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This disclosure relates to video coding and more particularly to techniques for performing entropy coding.

BACKGROUND ART

Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, laptop or desktop computers, tablet computers, digital recording devices, digital media players, video gaming devices, cellular telephones, including so-called smartphones, medical imaging devices, and the like. Digital video may be coded according to a video coding standard. Video coding standards may incorporate video compression techniques. Examples of video coding standards include ISO/IEC MPEG-4 Visual and ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC) and High-Efficiency Video Coding (HEVC). HEVC is described in High Efficiency Video Coding (HEVC), Rec. ITU-T H.265, December 2016, which is incorporated by reference, and referred to herein as ITU-T H.265. Extensions and improvements for ITU-T H.265 are currently being considered for the development of next generation video coding standards. For example, the ITU-T Video Coding Experts Group (VCEG) and ISO/IEC (Moving Picture Experts Group (MPEG) (collectively referred to as the Joint Video Exploration Team (JVET)) are studying the potential need for standardization of future video coding technology with a compression capability that significantly exceeds that of the current HEVC standard. The Joint Exploration Model 7 (JEM 7), Algorithm Description of Joint Exploration Test Model 7 (JEM 7), ISO/IEC JTC1/SC29/WG11 Document: JVET-G1001, July 2017, Torino, IT, which is incorporated by reference herein, describes the coding features that are under coordinated test model study by the JVET as potentially enhancing video coding technology beyond the capabilities of ITU-T H.265. It should be noted that the coding features of JEM 7 are implemented in JEM reference software. As used herein, the term JEM may collectively refer to algorithms included in JEM 7 and implementations of JEM reference software. Further, in response to a “Joint Call for Proposals on Video Compression with Capabilities beyond HEVC,” jointly issued by VCEG and MPEG, multiple descriptions of video coding were proposed by various groups at the 10^(th) Meeting of ISO/IEC JTC1/SC29/WG11 16-20 Apr. 2018, San Diego, Calif. As a result of the multiple descriptions of video coding, a draft text of a video coding specification is described in “Versatile Video Coding (Draft 1),” 10^(th) Meeting of ISO/IEC JTC1/SC29/WG11 16-20 Apr. 2018, San Diego, Calif., document JVET-J1001-v2, which is incorporated by reference herein, and referred to as JVET-J1001.

Video compression techniques enable data requirements for storing and transmitting video data to be reduced. Video compression techniques may reduce data requirements by exploiting the inherent redundancies in a video sequence. Video compression techniques may sub-divide a video sequence into successively smaller portions (i.e., groups of frames within a video sequence, a frame within a group of frames, slices within a frame, coding tree units (e.g., macroblocks) within a slice, coding blocks within a coding tree unit, etc.). Intra prediction coding techniques (e.g., intra-picture (spatial)) and inter prediction techniques (i.e., inter-picture (temporal)) may be used to generate difference values between a unit of video data to be coded and a reference unit of video data. The difference values may be referred to as residual data. Residual data may be coded as quantized transform coefficients. Syntax elements may relate residual data and a reference coding unit (e.g., intra-prediction mode indices, motion vectors, and block vectors). Residual data and syntax elements may be entropy coded. Entropy encoded residual data and syntax elements may be included in a compliant bitstream.

SUMMARY OF INVENTION

In one example, a decoder for decoding coded data, the decoder comprising: a decoding circuitry that decodes a first absolute level greater flag specifying whether an absolute value remainder syntax is present at a scanning position, wherein the decoding circuitry decodes a parity level flag specifying a parity of a transform coefficient level at the scanning position, if a value of a second absolute level greater flag is equal to a first value, and a value of the absolute value remainder syntax is equal to a value obtained by dividing an array representing an absolute values of transform coefficient levels by 2.

In one example, a method of decoding coded data, the method including: decoding a first absolute level greater flag specifying whether an absolute value remainder syntax is present at a scanning position, and decoding a parity level flag specifying a parity of a transform coefficient level at the scanning position, if a value of a second absolute level greater flag is equal to a first value, wherein a value of the absolute value remainder syntax is equal to a value obtained by dividing an array representing an absolute values of transform coefficient levels by 2.

In one example, a encoder for encoding data, the encoder comprising: a encoding circuitry that encodes a first absolute level greater flag specifying whether an absolute value remainder syntax is present at a scanning position, wherein the encoding circuitry encodes a parity level flag specifying a parity of a transform coefficient level at the scanning position, if a value of a second absolute level greater flag is equal to a first value, and a value of the absolute value remainder syntax is equal to a value obtained by dividing an array representing an absolute values of transform coefficient levels by 2.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating an example of a group of pictures coded according to a quad tree binary tree partitioning in accordance with one or more techniques of this disclosure.

FIG. 2A is a conceptual diagram illustrating examples of coding a block of video data in accordance with one or more techniques of this disclosure.

FIG. 2B is a conceptual diagram illustrating examples of coding a block of video data in accordance with one or more techniques of this disclosure.

FIG. 3 is a block diagram illustrating an example of a system that may be configured to encode and decode video data according to one or more techniques of this disclosure.

FIG. 4 is a block diagram illustrating an example of a video encoder that may be configured to encode video data according to one or more techniques of this disclosure.

FIG. 5 is a block diagram illustrating an example of a entropy encoder that may be configured to encode video data according to one or more techniques of this disclosure.

FIG. 6 is a block diagram illustrating an example of a video decoder that may be configured to decode video data according to one or more techniques of this disclosure.

FIG. 7 is a block diagram illustrating an example of a entropy decoder that may be configured to encode video data according to one or more techniques of this disclosure.

DESCRIPTION OF EMBODIMENTS

In general, this disclosure describes various techniques for coding video data. In particular, this disclosure describes techniques for coding transform coefficient level values. It should be noted that although techniques of this disclosure are described with respect to ITU-T H.264, ITU-T H.265, and JEM, the techniques of this disclosure are generally applicable to video coding. For example, the coding techniques described herein may be incorporated into video coding systems, (including video coding systems based on future video coding standards) including block structures, intra prediction techniques, inter prediction techniques, transform techniques, filtering techniques, and/or entropy coding techniques other than those included in ITU-T H.265 and JEM. Thus, reference to ITU-T H.264, ITU-T H.265, and/or JEM is for descriptive purposes and should not be construed to limit the scope of the techniques described herein. Further, it should be noted that incorporation by reference of documents herein is for descriptive purposes and should not be construed to limit or create ambiguity with respect to terms used herein. For example, in the case where an incorporated reference provides a different definition of a term than another incorporated reference and/or as the term is used herein, the term should be interpreted in a manner that broadly includes each respective definition and/or in a manner that includes each of the particular definitions in the alternative.

In one example, a method comprises determining whether a coefficient level value is equal to one, and in the case where the coefficient level value is equal to one indicating that the coefficient level value is equal to one by signaling values for a first flag and a second flag, in the case where the coefficient level value is greater than one determining whether the coefficient level value is greater than or equal to three, in the case where the coefficient level value is not greater than or equal to three, indicating that the coefficient level value is equal to two by signaling values for the first flag, the second flag, and a third flag, in the case where the coefficient level value is greater than or equal to three, indicating a value of the coefficient level by signaling values for the first flag, the second flag, the third flag, and a fourth flag.

In one example, a device comprises one or more processors configured to determine whether a coefficient level value is equal to one, and in the case where the coefficient level value is equal to one indicate that the coefficient level value is equal to one by signaling values for a first flag and a second flag, in the case where the coefficient level value is greater than one determine whether the coefficient level value is greater than or equal to three, in the case where the coefficient level value is not greater than or equal to three, indicate that the coefficient level value is equal to two by signaling values for the first flag, the second flag, and a third flag, in the case where the coefficient level value is greater than or equal to three, indicate a value of the coefficient level by signaling values for the first flag, the second flag, the third flag, and a fourth flag.

In one example, a non-transitory computer-readable storage medium comprises instructions stored thereon that, when executed, cause one or more processors of a device to determine whether a coefficient level value is equal to one, and in the case where the coefficient level value is equal to one indicate that the coefficient level value is equal to one by signaling values for a first flag and a second flag, in the case where the coefficient level value is greater than one determine whether the coefficient level value is greater than or equal to three, in the case where the coefficient level value is not greater than or equal to three, indicate that the coefficient level value is equal to two by signaling values for the first flag, the second flag, and a third flag, in the case where the coefficient level value is greater than or equal to three, indicate a value of the coefficient level by signaling values for the first flag, the second flag, the third flag, and a fourth flag.

In one example, an apparatus comprises means for determining whether a coefficient level value is equal to one, and in the case where the coefficient level value is equal to one means for indicating that the coefficient level value is equal to one by signaling values for a first flag and a second flag, in the case where the coefficient level value is greater than one means for determining whether the coefficient level value is greater than or equal to three, in the case where the coefficient level value is not greater than or equal to three, means for indicating that the coefficient level value is equal to two by signaling values for the first flag, the second flag, and a third flag, in the case where the coefficient level value is greater than or equal to three, means for indicating a value of the coefficient level by signaling values for the first flag, the second flag, the third flag, and a fourth flag.

In one example, a method comprises parsing a first and second flag included in a bitstream, determining that a coefficient level value is greater than one based on the values of the parsed first and second flags, parsing a third and fourth flag included in the bitstream, determining whether the coefficient level value is an odd number greater than or equal to three or an even number greater than or equal to four based on the values of the parsed third and fourth flag.

In one example, a device comprises one or more processors configured to parse a first and second flag included in a bitstream, determine that a coefficient level value is greater than one based on the values of the parsed first and second flags, parse a third and fourth flag included in the bitstream, determine whether the coefficient level value is an odd number greater than or equal to three or an even number greater than or equal to four based on the values of the parsed third and fourth flag.

In one example, a non-transitory computer-readable storage medium comprises instructions stored thereon that, when executed, cause one or more processors of a device to parse a first and second flag included in a bitstream, determine that a coefficient level value is greater than one based on the values of the parsed first and second flags, parse a third and fourth flag included in the bitstream, determine whether the coefficient level value is an odd number greater than or equal to three or an even number greater than or equal to four based on the values of the parsed third and fourth flag.

In one example, an apparatus comprises means for parsing a first and second flag included in a bitstream, means for determining that a coefficient level value is greater than one based on the values of the parsed first and second flags, means for parsing a third and fourth flag included in the bitstream, means for determining whether the coefficient level value is an odd number greater than or equal to three or an even number greater than or equal to four based on the values of the parsed third and fourth flag.

The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

Video content typically includes video sequences comprised of a series of frames (or pictures). A series of frames may also be referred to as a group of pictures (GOP). Each video frame or picture may include a plurality of slices or tiles, where a slice or tile includes a plurality of video blocks. As used herein, the term video block may generally refer to an area of a picture or may more specifically refer to the largest array of sample values that may be predictively coded, sub-divisions thereof, and/or corresponding structures. Further, the term current video block may refer to an area of a picture being encoded or decoded. A video block may be defined as an array of sample values that may be predictively coded. It should be noted that in some cases pixel values may be described as including sample values for respective components of video data, which may also be referred to as color components, (e.g., luma (Y) and chroma (Cb and Cr) components or red, green, and blue components). It should be noted that in some cases, the terms pixel value and sample value are used interchangeably. Video blocks are ordered within a picture according to a scan pattern (e.g., a raster scan). A video encoder may perform predictive encoding on video blocks and sub-divisions thereof. Video blocks and sub-divisions thereof may be referred to as nodes.

A video sampling format, which may also be referred to as a chroma format, may define the number of chroma samples included in a CU with respect to the number of luma samples included in a CU. For example, for the 4:2:0 sampling format, the sampling rate for the luma component is twice that of the chroma components for both the horizontal and vertical directions. As a result, for a CU formatted according to the 4:2:0 format, the width and height of an array of samples for the luma component are twice that of each array of samples for the chroma components. As described above, a CU is typically defined according to the number of horizontal and vertical luma samples. For a CU formatted according to the 4:2:2 format, the width of an array of samples for the luma component is twice that of the width of an array of samples for each chroma component, but the height of the array of samples for the luma component is equal to the height of an array of samples for each chroma component. Further, for a CU formatted according to the 4:4:4 format, an array of samples for the luma component has the same width and height as an array of samples for each chroma component.

ITU-T H.264 specifies a macroblock including 16×16 luma samples. That is, in ITU-T H.264, a picture is segmented into macroblocks. ITU-T H.265 specifies an analogous Coding Tree Unit (CTU) structure (which may be referred to as a largest coding unit (LCU)). In ITU-T H.265, pictures are segmented into CTUs. In ITU-T H.265, for a picture, a CTU size may be set as including 16×16, 32×32, or 64×64 luma samples. In ITU-T H.265, a CTU is composed of respective Coding Tree Blocks (CTB) for each component of video data (e.g., luma (Y) and chroma (Cb and Cr). It should be noted that video having one luma component and the two corresponding chroma components may be described as having two channels, i.e., a luma channel and a chroma channel. Further, in ITU-T H.265, a CTU may be partitioned according to a quadtree (QT) partitioning structure, which results in the CTBs of the CTU being partitioned into Coding Blocks (CB). That is, in ITU-T H.265, a CTU may be partitioned into quadtree leaf nodes. According to ITU-T H.265, one luma CB together with two corresponding chroma CBs and associated syntax elements are referred to as a coding unit (CU). In ITU-T H.265, a minimum allowed size of a CB may be signaled. In ITU-T H.265, the smallest minimum allowed size of a luma CB is 8×8 luma samples. In ITU-T H.265, the decision to code a picture area using intra prediction or inter prediction is made at the CU level.

In ITU-T H.265, a CU is associated with a prediction unit (PU) structure having its root at the CU. In ITU-T H.265, PU structures allow luma and chroma CBs to be split for purposes of generating corresponding reference samples. That is, in ITU-T H.265, luma and chroma CBs may be split into respective luma and chroma prediction blocks (PBs), where a PB includes a block of sample values for which the same prediction is applied. In ITU-T H.265, a CB may be partitioned into 1, 2, or 4 PBs. ITU-T H.265 supports PB sizes from 64×64 samples down to 4×4 samples. In ITU-T H.265, square PBs are supported for intra prediction, where a CB may form the PB or the CB may be split into four square PBs (i.e., intra prediction PB types include M×M or M/2×M/2, where M is the height and width of the square CB). In ITU-T H.265, in addition to the square PBs, rectangular PBs are supported for inter prediction, where a CB may by halved vertically or horizontally to form PBs (i.e., inter prediction PB types include M×M, M/2×M/2, M/2×M, or M×M/2). Further, it should be noted that in ITU-T H.265, for inter prediction, four asymmetric PB partitions are supported, where the CB is partitioned into two PBs at one quarter of the height (at the top or the bottom) or width (at the left or the right) of the CB (i.e., asymmetric partitions include M/4×M left, M/4×M right, M×M/4 top, and M×M/4 bottom). Intra prediction data (e.g., intra prediction mode syntax elements) or inter prediction data (e.g., motion data syntax elements) corresponding to a PB is used to produce reference and/or predicted sample values for the PB.

JEM specifies a CTU having a maximum size of 256×256 luma samples. JEM specifies a quadtree plus binary tree (QTBT) block structure. In JEM, the QTBT structure enables quadtree leaf nodes to be further partitioned by a binary tree (BT) structure. That is, in JEM, the binary tree structure enables quadtree leaf nodes to be recursively divided vertically or horizontally. FIG. 1 illustrates an example of a CTU (e.g., a CTU having a size of 256×256 luma samples) being partitioned into quadtree leaf nodes and quadtree leaf nodes being further partitioned according to a binary tree. That is, in FIG. 1 dashed lines indicate additional binary tree partitions in a quadtree. Thus, the binary tree structure in JEM enables square and rectangular leaf nodes, where each leaf node includes a CB. As illustrated in FIG. 1 , a picture included in a GOP may include slices, where each slice includes a sequence of CTUs and each CTU may be partitioned according to a QTBT structure. FIG. 1 illustrates an example of QTBT partitioning for one CTU included in a slice. In JEM, CBs are used for prediction without any further partitioning. That is, in JEM, a CB may be a block of sample values on which the same prediction is applied. Thus, a JEM QTBT leaf node may be analogous a PB in ITU-T H.265.

For intra prediction coding, an intra prediction mode may specify the location of reference samples within a picture. In ITU-T H.265, defined possible intra prediction modes include a planar (i.e., surface fitting) prediction mode (predMode: 0), a DC (i.e., flat overall averaging) prediction mode (predMode: 1), and 33 angular prediction modes (predMode: 2-34). In JEM, defined possible intra-prediction modes include a planar prediction mode (predMode: 0), a DC prediction mode (predMode: 1), and 65 angular prediction modes (predMode: 2-66). It should be noted that planar and DC prediction modes may be referred to as non-directional prediction modes and that angular prediction modes may be referred to as directional prediction modes. It should be noted that the techniques described herein may be generally applicable regardless of the number of defined possible prediction modes.

For inter prediction coding, a motion vector (MV) identifies reference samples in a picture other than the picture of a video block to be coded and thereby exploits temporal redundancy in video. For example, a current video block may be predicted from reference block(s) located in previously coded frame(s) and a motion vector may be used to indicate the location of the reference block. A motion vector and associated data may describe, for example, a horizontal component of the motion vector, a vertical component of the motion vector, a resolution for the motion vector (e.g., one-quarter pixel precision, one-half pixel precision, one-pixel precision, two-pixel precision, four-pixel precision), a prediction direction and/or a reference picture index value. Further, a coding standard, such as, for example ITU-T H.265, may support motion vector prediction. Motion vector prediction enables a motion vector to be specified using motion vectors of neighboring blocks. Examples of motion vector prediction include advanced motion vector prediction (AMVP), temporal motion vector prediction (TMVP), so-called “merge” mode, and “skip” and “direct” motion inference. Further, JEM supports advanced temporal motion vector prediction (ATMVP) and Spatial-temporal motion vector prediction (STMVP).

As described above, intra prediction data or inter prediction data is used to produce reference sample values for a block of sample values. The difference between sample values included in a current PB, or another type of picture area structure, and associated reference samples (e.g., those generated using a prediction) may be referred to as residual data. Residual data may include respective arrays of difference values corresponding to each component of video data. Residual data may be in the pixel domain. A transform, such as, a discrete cosine transform (DCT), a discrete sine transform (DST), an integer transform, a wavelet transform, or a conceptually similar transform, may be applied to an array of difference values to generate transform coefficients. In some cases, a transform process may include rotation, and/or performance of one or more one dimensional transforms. It should be noted that in ITU-T H.265, a CU is associated with a transform unit (TU) structure having its root at the CU level. That is, in ITU-T H.265, an array of difference values may be sub-divided for purposes of generating transform coefficients (e.g., four 8×8 transforms may be applied to a 16×16 array of residual values). For each component of video data, such sub-divisions of difference values may be referred to as Transform Blocks (TBs). It should be noted that in ITU-T H.265, TBs are not necessarily aligned with PBs. Further, it should be noted that in ITU-T H.265, TBs may have the following sizes 4×4, 8×8, 16×16, and 32×32.

It should be noted that in JEM, residual values corresponding to a CB are used to generate transform coefficients without further partitioning. That is, in JEM a QTBT leaf node may be analogous to both a PB and a TB in ITU-T H.265. It should be noted that in JEM, a core transform and a subsequent secondary transforms may be applied (in the video encoder) to generate transform coefficients. For a video decoder, the order of transforms is reversed. Further, in JEM, whether a secondary transform is applied to generate transform coefficients may be dependent on a prediction mode.

A quantization process may be performed on transform coefficients or residual sample values directly, e.g., in the case of palette coding quantization. Quantization approximates transform coefficients by amplitudes restricted to a set of specified values. Quantization essentially scales transform coefficients in order to vary the amount of data required to represent a group of transform coefficients. Quantization may include division of transform coefficients (or resulting values of addition of an offset value to transform coefficients) by a quantization scaling factor and any associated rounding functions (e.g., rounding to the nearest integer). Quantized transform coefficients may be referred to as coefficient level values. Inverse quantization (or “dequantization”) may include multiplication of coefficient level values by the quantization scaling factor, and any reciprocal rounding or offset addition operations. It should be noted that as used herein the term quantization process in some instances may refer to division by a scaling factor to generate level values and multiplication by a scaling factor to recover transform coefficients in some instances. That is, a quantization process may refer to quantization in some cases and inverse quantization in some cases. Further, it should be noted that although in some of the examples below quantization processes are described with respect to arithmetic operations associated with decimal notation, such descriptions are for illustrative purposes and should not be construed as limiting. For example, the techniques described herein may be implemented in a device using binary operations and the like. For example, multiplication and division operations described herein may be implemented using bit shifting operations and the like.

With respect to the equations used herein, the following arithmetic operators may be used:

-   -   + Addition     -   − Subtraction     -   * Multiplication, including matrix multiplication     -   x^(y) Exponentiation. Specifies x to the power of y. In other         contexts, such notation is used for superscripting not intended         for interpretation as exponentiation.     -   / Integer division with truncation of the result toward zero.         For example, 7/4 and −7/−4 are truncated to 1 and −7/4 and 7/−4         are truncated to −1.     -   ÷ Used to denote division in mathematical equations where no         truncation or rounding is intended.

$\frac{x}{y}$

-   -   Used to denote division in mathematical equations where no         truncation or rounding is intended.     -   x % y Modulus. Remainder of x divided by y, defined only for         integers x and y with x>=0 and y>0.

Further, the following logical operators may be used:

-   -   x&&y Boolean logical “and” of x and y     -   x∥y Boolean logical “or” of x and y     -   ! Boolean logical “not”     -   x?y:z If x is TRUE or not equal to 0, evaluates to the value of         y; otherwise, evaluates to the value of z.

Further, the following relational operators may be used:

-   -   > Greater than     -   >= Greater than or equal to     -   < Less than     -   <= Less than or equal to     -   == Equal to     -   != Not equal to

Further, the following bit-wise operators may be used:

-   -   & Bit-wise “and”. When operating on integer arguments, operates         on a two's complement representation of the integer value. When         operating on a binary argument that contains fewer bits than         another argument, the shorter argument is extended by adding         more significant bits equal to 0.     -   | Bit-wise “or”. When operating on integer arguments, operates         on a two's complement representation of the integer value. When         operating on a binary argument that contains fewer bits than         another argument, the shorter argument is extended by adding         more significant bits equal to 0.     -   {circumflex over ( )} A Bit-wise “exclusive or”. When operating         on integer arguments, operates on a two's complement         representation of the integer value. When operating on a binary         argument that contains fewer bits than another argument, the         shorter argument is extended by adding more significant bits         equal to 0.     -   x>>y Arithmetic right shift of a two's complement integer         representation of x by y binary digits. This function is defined         only for non-negative integer values of y. Bits shifted into the         most significant bits (MSBs) as a result of the right shift have         a value equal to the MSB of x prior to the shift operation.     -   x<<y Arithmetic left shift of a two's complement integer         representation of x by y binary digits. This function is defined         only for non-negative integer values of y. Bits shifted into the         least significant bits (LSBs) as a result of the left shift have         a value equal to 0.

FIGS. 2A-2B are conceptual diagrams illustrating examples of coding a block of video data. As illustrated in FIG. 2A, a current block of video data (e.g., a CB corresponding to a video component) is encoded by generating a residual by subtracting a set of prediction values from the current block of video data, performing a transformation on the residual, and quantizing the transform coefficients to generate level values. As illustrated in FIG. 2B, the current block of video data is decoded by performing inverse quantization on level values, performing an inverse transform, and adding a set of prediction values to the resulting residual. It should be noted that in the examples in FIGS. 2A-2B, the sample values of the reconstructed block differs from the sample values of the current video block that is encoded. In this manner, coding may said to be lossy. However, the difference in sample values may be considered acceptable or imperceptible to a viewer of the reconstructed video.

Further, as illustrated in FIGS. 2A-2B, coefficient level values are generated using an array of scaling factors. In ITU-T H.265, an array of scaling factors is generated by selecting a scaling matrix and multiplying each entry in the scaling matrix by a quantization scaling factor. In ITU-T H.265, a scaling matrix is selected based in part on a prediction mode and a color component, where scaling matrices of the following sizes are defined: 4×4, 8×8, 16×16, and 32×32. It should be noted that in some examples, a scaling matrix may provide the same value for each entry (i.e., all coefficients are scaled according to a single value). In ITU-T H.265, the value of a quantization scaling factor, may be determined by a quantization parameter, QP. In ITU-T H.265, for a bit-depth of 8-bits, the QP can take 52 values from 0 to 51 and a change of 1 for QP generally corresponds to a change in the value of the quantization scaling factor by approximately 12%. Further, in ITU-T H.265, a QP value for a set of transform coefficients may be derived using a predictive quantization parameter value (which may be referred to as a predictive QP value or a QP predictive value) and an optionally signaled quantization parameter delta value (which may be referred to as a QP delta value or a delta QP value). In ITU-T H.265, a quantization parameter may be updated for each CU and a respective quantization parameter may be derived for each of the luma and chroma channels.

Referring again to FIG. 2A, coefficient level values are coded into a bitstream. Coefficient level values and syntax elements (e.g., syntax elements indicating a coding structure for a video block) may be entropy coded according to an entropy coding technique. An entropy coding process includes coding values of syntax elements using lossless data compression algorithms. Examples of entropy coding techniques include content adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), probability interval partitioning entropy coding (PIPE), and the like. Entropy encoded quantized transform coefficients and corresponding entropy encoded syntax elements may form a compliant bitstream that can be used to reproduce video data at a video decoder. An entropy coding process, for example, CABAC, may include performing a binarization on syntax elements. Binarization refers to the process of converting a value of a syntax element into a series of one or more bits. These bits may be referred to as “bins.” Binarization may include one or a combination of the following coding techniques: fixed length coding, unary coding, truncated unary coding, truncated Rice coding, Golomb coding, k-th order exponential Golomb coding, and Golomb-Rice coding. For example, binarization may include representing the integer value of 5 for a syntax element as 00000101 using an 8-bit fixed length binarization technique or representing the integer value of 5 as 11110 using a unary coding binarization technique. As used herein each of the terms fixed length coding, unary coding, truncated unary coding, truncated Rice coding, Golomb coding, k-th order exponential Golomb coding, and Golomb-Rice coding may refer to general implementations of these techniques and/or more specific implementations of these coding techniques. For example, a Golomb-Rice coding implementation may be specifically defined according to a video coding standard, for example, ITU-T H.265.

In the example of CABAC in ITU-T H.265, for a particular bin, a context model is used to determine a context index for the bin. A context model is essential a probability state model for a bin and a context index provides a most probable state (MPS) value for the bin (i.e., an MPS for a bin is one of 0 or 1) and a probability value of the bin being the MPS and/or least probable state (LPS) at a given state of arithmetic coding. For example, a context index may indicate, at a current state, that the MPS of a bin is 0 and the probability of the bin being 1 (i.e., the LPS) is 0.3. It should be noted that a context model may be selected based on values of previously coded syntax elements. For example, values of syntax elements associated with neighboring video blocks may be used to determine a context model associated with a syntax element corresponding to a current video block.

Binary arithmetic coding codes a series of 0's and 1's based on the principle of recursive interval subdivision. Essentially, for a binary string (b₁, . . . , b_(N)), for an interval having an initial width (range) R₀, for (b₁, . . . , b_(N)), R₀ is recursively divided as follows:

For i = (1,...,N),  if b_(i) equals LPS:   R_(i) = pLPS_(i)*R_(i−1), otherwise   R_(i) = R_(i−1) − pLPS_(i)*R_(i−1),

-   -   Where,     -   LPS is the value of the least probably symbol, and     -   pLPS_(i) is the estimated probability of b_(i) being the LPS.

As illustrated above, R, is determined based on whether the observed value of b_(i) is the MPS or LPS. For example, for b₁ if R₀ is 512, the LPS is 0, and pLPS_(I)*R₀ is 158, if b₁ is observed to be 1, R₁=354 and if b₁ is observed to be 0, R₁=158. In ITU-T H.265, a context index provides an MPS value for a bin and a probability value of the bin being the LPS, where the probability value of the bin being the LPS (i.e., pLPS) is indicated by one of 64 probability states. In particular, in ITU-T H.265, a probability state index variable, pStateIdx, is indexed such that, pStateIdx=0 corresponds to a maximum LPS probability value, and decreasing LPS probabilities are indexed to higher values of pStateIdx. Further, in ITU-T H.265, R₀ is 512 which can be represented by 9-bits. However, R_(i) is quantized to a set {Q1, . . . , Q4} such that all possible values of pLPS_(i)*R_(i−1) are pre-computed and indexed according to a 64×4 look-up table.

During encoding, after an interval for R_(i) is determined, i.e., based on pLPS_(i) and the observed value of b_(i), a renormalization process occurs. A renormalization process essentially determines whether bits are output (e.g., written to a bitstream) based on the value of R_(i). Essentially, in renormalization, if R_(i) falls below a threshold value, and R_(i) is doubled and a bit value may be output. For example, in encoder side renormalization process described in ITU-T H.265, a determination is made if R_(i) is less than 256. If R_(i) is not less than 256, no bits are written to the bitstream and R_(i+1) is computed for b_(i+1), using R_(i). If R_(i) is less than 256, a 0-bit, a 1-bit, or no bit is conditionally written to the bitstream based on the lower end of the sub-interval, and R_(i) is doubled, and R_(i+1) is computed for b_(i+1) (i.e., based on the doubled value of R_(i)). A binary decoder receiving the output bits (i.e., the arithmetic code) recovers the binary string (b₁, . . . , b_(N)) by performing the same interval sub-division at each b_(i) as an encoder and by comparing subsets of the arithmetic code to R_(i) values.

In ITU-T H.265, the observed value of a bin is used to update the context index. ITU-T H.265 provides the following with respect to updating the context index based on the determined value of the bin:

if( binVal = = valMps )  pStateIdx = transIdxMps( pStateIdx ) else {  if( pStateIdx = = 0 )   valMps = 1 − valMps  pStateIdx = transIdxLps( pStateIdx ) }

-   -   Where,     -   valMps is the value of the MPS for the bin; and     -   transIdxMps 0 and transIdxLps0 are a defined set of transition         rules as provided in Table 1.

TABLE 1 pStateIdx 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 transIdxLps 0 0 1 2 2 4 4 5 6  7  8  9  9 11 11 12 transIdxMps 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 pStateIdx 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 transIdxLps 13 13 15 15 16 16 18 18 19 19 21 21 22 22 23 24 transIdxMps 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 pStateIdx 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 transIdxLps 24 25 26 26 27 27 28 29 29 30 30 30 31 32 32 33 transIdxMps 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 pStateIdx 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 transIdxLps 33 33 34 34 35 35 35 36 36 36 37 37 37 38 38 63 transIdxMps 49 50 51 52 53 54 55 56 57 58 59 60 61 62 62 63

Thus, in ITU-T H.265, if the bin value is determined to be equal to the MPS, the LPS probability value is decreased. If the bin value is determined to be equal to the LPS, the LPS probability value is increased and further, if the current probability state pLPS is 0.5 (i.e., pStateIdx equals 0), a LPS inversion occurs (i.e., the previous LPS value becomes the MPS). It should be noted, that according to ITU-T H.265, some syntax elements are entropy coded using arithmetic coding according to equal probability states, such coding may be referred to as bypass coding. The probability estimation provided in ITU-T H.265 has a relatively low complexity. Improved probability estimations (i.e., more accurate) with higher complexity have been proposed for use in binary arithmetic coding.

As described above, coefficient level values are coded into a bitstream. In ITU-T H.265, a coefficient level value is indicated according to the syntax illustrated in Table 2.

TABLE 2 residual_coding( x0, y0, log2TrafoSize, cIdx ) { ...   xS = ScanOrder[ log2TrafoSize − 2 ][ scanIdx ][ lastSubBlock ][ 0 ]   yS = ScanOrder[ log2TrafoSize − 2 ][ scanIdx ][ lastSubBlock ][ 1 ]   xC = ( xS << 2 ) + ScanOrder[ 2 ][ scanIdx ][ lastScanPos ][ 0 ]   yC = ( yS << 2 ) + ScanOrder[ 2 ][ scanIdx ][ lastScanPos ][ 1 ]  } while( ( xC != LastSignificantCoeffX ) | | ( yC !=  LastSignificantCoeffY ) )  for( i = lastSubBlock; i >= 0; i− − ) {   xS = ScanOrder[ log2TrafoSize − 2 ][ scanIdx ][ i ][ 0 ]   yS = ScanOrder[ log2TrafoSize − 2 ][ scanIdx ][ i ][ 1 ]   inferSbDcSigCoeffFlag = 0   if( ( i < lastSubBlock ) && ( i > 0 ) ) {    coded_sub_block_flag[ xS ][ yS ]    inferSbDcSigCoeffFlag = 1   }   for( n = ( i = = lastSubBlock ) ? lastScanPos − 1 : 15; n >= 0; n− −   ) {    xC = ( xS << 2 ) + ScanOrder[ 2 ][ scanIdx ][ n ][ 0 ]    yC = ( yS << 2 ) + ScanOrder[ 2 ][ scanIdx ][ n ][ 1 ]    if( coded_sub_block_flag[ xS ][ yS ] && ( n > 0 | |    !inferSbDcSigCoeffFlag ) ) {     sig_coeff_flag[ xC ][ yC ]     if( sig_coeff_flag[ xC ][ yC ] )      inferSbDcSigCoeffFlag = 0    }   }   firstSigScanPos = 16   lastSigScanPos = −1   numGreater1Flag = 0   lastGreater1ScanPos = −1   for( n = 15; n >= 0; n− − ) {    xC = ( xS << 2 ) + ScanOrder[ 2 ][ scanIdx ][ n ][ 0 ]    yC = ( yS << 2 ) + ScanOrder[ 2 ][ scanIdx ][ n ][ 1 ]    if( sig_coeff_flag[ xC ][ yC ] ) {     if( numGreater1Flag < 8 ) {      coeff_abs_level_greater1_flag[ n ]      numGreater1Flag++      if( coeff_abs_level_greater1_flag[ n ] &&      lastGreater1ScanPos = = −1 )       lastGreater1ScanPos = n      else if( coeff_abs_level_greater1_flag[ n ] )       escapeDataPresent = 1     } else      escapeDataPresent = 1     if( lastSigScanPos = = −1 )      lastSigScanPos = n     firstSigScanPos = n    }   } ...   if( lastGreater1ScanPos != −1 ) {    coeff_abs_level_greater2_flag[ lastGreater1ScanPos ]    if( coeff_abs_level_greater2_flag[ lastGreater1ScanPos ] )     escapeDataPresent = 1   }   for( n = 15; n >= 0; n− − ) {    xC = ( xS << 2 ) + ScanOrder[ 2 ][ scanIdx ][ n ][ 0 ]    yC = ( yS << 2 ) + ScanOrder[ 2 ][ scanIdx ][ n ][ 1 ]    if( sig_coeff_flag[ xC ][ yC ] &&     ( !sign_data_hiding_enabled_flag | | !signHidden | | ( n != firstSigScanPos ) ) )     coeff_sign_flag[ n ]   }   numSigCoeff = 0   sumAbsLevel = 0   for( n = 15; n >= 0; n− − ) {    xC = ( xS << 2 ) + ScanOrder[ 2 ][ scanIdx ][ n ][ 0 ]    yC = ( yS << 2 ) + ScanOrder[ 2 ][ scanIdx ][ n ][ 1 ]    if( sig_coeff_flag[ xC ][ yC ] ) {     baseLevel = 1 + coeff_abs_level_greater1_flag[ n ] +        coeff_abs_level_greater2_flag[ n ]     if( baseLevel = = ( ( numSigCoeff < 8 ) ?         ( (n = = lastGreater1ScanPos) ? 3 : 2 ) : 1 ) )      coeff_abs_level_remaining[ n ]     TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] =      ( coeff_abs_level_remaining[ n ] + baseLevel ) * ( 1 − 2 *      coeff_sign_flag[ n ] ) ... }

With respect to Table 2, ITU-T H.265, provides the following semantics:

coded_sub_block_flag[xS][yS] specifies the following for the sub-block at location (xS, yS) within the current transform block, where a sub-block is a (4×4) array of 16 transform coefficient levels:

-   -   If coded_sub_block_flag[xS][yS] is equal to 0, the 16 transform         coefficient levels of the sub-block at location (xS, yS) are         inferred to be equal to 0.     -   Otherwise (coded_sub_block_flag[xS][yS] is equal to 1), the         following applies:         -   If (xS, yS) is equal to (0, 0) and (LastSignificantCoeffX,             LastSignificantCoeffY) is not equal to (0, 0), at least one             of the 16 sig_coeff_flag syntax elements is present for the             sub-block at location (xS, yS).         -   Otherwise, at least one of the 16 transform coefficient             levels of the sub-block at location (xS, yS) has a non zero             value.

When coded_sub_block_flag[xS ][yS ] is not present, it is inferred as follows:

-   -   If one or more of the following conditions are true,         coded_sub_block_flag[xS][yS] is inferred to be equal to 1:         -   (xS, yS) is equal to (0, 0)         -   (xS, yS) is equal to (LastSignificantCoeffX>>2,             LastSignificantCoeffY>>2)     -   Otherwise, coded_sub_block_flag[xS ][yS] is inferred to be equal         to 0.

sig_coeff_flag[xC][yC] specifies for the transform coefficient location (xC, yC) within the current transform block whether the corresponding transform coefficient level at the location (xC, yC) is non-zero as follows:

-   -   If sig_coeff_flag[xC][yC] is equal to 0, the transform         coefficient level at the location (xC, yC) is set equal to 0.     -   Otherwise (sig_coeff_flag[xC][yC] is equal to 1), the transform         coefficient level at the location (xC, yC) has a non-zero value.         -   When sig_coeff_flag[xC][yC] is not present, it is inferred             as follows:     -   If (xC, yC) is the last significant location         (LastSignificantCoeffX, LastSignificantCoeffY) in scan order or         all of the following conditions are true, sig_coeff_flag[xC][yC]         is inferred to be equal to 1:         -   (xC&3, yC&3) is equal to (0, 0)         -   inferSbDcSigCoeffFlag is equal to 1         -   coded_sub_block_flag[xS][yS] is equal to 1     -   Otherwise, sig_coeff_flag[xC][yC] is inferred to be equal to 0.

coeff_abs_level_greater1_flag[n] specifies for the scanning position n whether there are absolute values of transform coefficient levels greater than 1.

When coeff abs_level_greater1_flag[n] is not present, it is inferred to be equal to 0.

coeff_abs_level_greater2_flag[n] specifies for the scanning position n whether there are absolute values of transform coefficient levels greater than 2.

When coeff abs_level_greater2_flag[n] is not present, it is inferred to be equal to 0.

coeff_sign_flag[n] specifies the sign of a transform coefficient level for the scanning position n as follows:

-   -   If coeff_sign_flag[n] is equal to 0, the corresponding transform         coefficient level has a positive value.     -   Otherwise (coeff_sign_flag[n] is equal to 1), the corresponding         transform coefficient level has a negative value.

When coeff_sign_flag[n] is not present, it is inferred to be equal to 0.

coeff_abs_level_remaining[n] is the remaining absolute value of a transform coefficient level that is coded with Golomb-Rice code at the scanning position n.

When coeff abs_level_remaining[n] is not present, it is inferred to be equal to 0.

Table 3 provides a summary of possible level values of a coefficient in a sub-block having significant coefficients according to values of sig_coeff_flag, coeff_abs_level_greater1_flag, coeff_abs_level_greater2_flag, and coeff_abs_level_remaining in ITU-T H.265.

TABLE 3 sig_coeff_flag coeff_abs_level_greater1_flag coeff_abs_level_greater2_flag coeff_abs_level_remaining Coefficient Level Value 0 Not Signaled Not Signaled Not Signaled 0 1 0 Not Signaled Not Signaled (1 − 2 * coeff_sign_flag) 1 1 0 Not Signaled 2*(1 − 2 * coeff_sign_flag) 1 1 1 Signaled (coeff_abs_level_remaining + 3]) * (1 − 2 * coeff_sign_flag[n])

It should be noted that each of coded_sub_block_flag, sig_coeff_flag, coeff_abs_level_greater1_flag, coeff_abs_level_greater2_flag, and coeff_sign_flag have a 1-bit fixed length binarization and ITU-T H.265 provides a specific binarization for coeff_abs_level_remaining. Further, ITU-T H.265 provides where coeff_sign_flag and coeff_abs_level_remaining are bypass coded and where one of four contexts is derived for coded_sub_block_flag, one of 44 contexts is derived for sig_coeff_flag, one of 24 contexts is derived for coeff_abs_level_greater1_flag, and one of six contexts is selected for coeff_abs_level_greater2_flag. For the sake of brevity, details of the specific binarization for coeff_abs_level_remaining and the derivation of contexts for coded_sub_block_flag, sig_coeff_flag, coeff_abs_level_greater1_flag, and coeff_abs_level_greater2_flag. However, reference in made to the relevant sections in ITU-T H.265.

“Non-CE7: Alternative Entropy Coding for Dependent Quantization,” 11th Meeting of ISO/IEC JTC1/SC29/WG11 10-18 Jul. 2018, Ljubljana, SI, document JVET-K0072-v2, which is incorporated by reference herein, and referred to as JVET-K0072, describes an implementation of coding coefficient level values. In JVET-K0072, the transform coefficient levels of a sub-block are coded in the following four passes over the scan positions:

-   -   pass 1: coding of significance (sig_coeff_flag), parity         (par_level_flag), and greater 1 flag (rem_abs_gt1_flag) in         coding order. The parity and greater 1 flags are only present if         sig_coeff_flag is equal to 1. The context for the greater 1 flag         does not depend on the directly preceding parity flag, and the         context of the sig_coeff_flag does not dependent on the value of         the directly preceding rem_abs_gt1_flag (when the previous         sig_coeff_flag is equal to 1);     -   pass 2: coding of greater 2 flags (rem_abs_gt2_flag) for all         scan positions with rem_abs_gt1_flag equal to 1. The context         models do not depend on any data coded in this 2^(nd) pass.     -   pass 3: coding of the syntax element abs_remainder for all scan         positions with rem_abs_gt2_flag equal to 1. The non-binary         syntax element is binarized and the resulting bins are coded in         the bypass mode of the arithmetic coding engine;     -   pass 4: coding of the signs (sign_flag) for all scan positions         with sig_coeff_flag equal to 1.

In JVET-K0072, a coefficient level value is indicated according to the syntax illustrated in Table 4.

TABLE 4 residual_coding( x0, y0, log2TrafoSizeX, log2TrafoSizeY, cIdx, stateTransTable ) { ... xS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY − log2SbSize ] [ scanIdx ][ lastSubBlock ][ 0 ] yS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY − log2SbSize ] [ scanIdx ][ lastSubBlock ][ 1 ] xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ lastScanPos ][ 0 ] yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ lastScanPos ][ 1 ]  } while( ( xC != LastSignificantCoeffX ) | | ( yC !=  LastSignificantCoeffY ) )  state = 0  for( i = lastSubBlock; i >= 0; i− − ) {   xS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY −   log2SbSize ]       [ scanIdx ][ lastSubBlock ][ 0 ]   yS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY −   log2SbSize ]       [ scanIdx ][ lastSubBlock ][ 1 ]   inferSbDcSigCoeffFlag = 0   if( ( i < lastSubBlock ) && ( i > 0 ) ) {    coded_sub_block_flag[ xS ][ yS ]    inferSbDcSigCoeffFlag = 1   }   //===== first pass: sig, par, gt1 =====   for( n = ( i = = lastSubBlock ) ? lastScanPos − 1 : numSbCoeff − 1; n >= 0; n− − ) {    xC = ( xS << log2SbSize ) +       ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ n ][ 0 ]    yC = ( yS << log2SbSize ) +       ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ n ][ 1 ]    if( coded_sub_block_flag[ xS ][ yS ] && ( n > 0 | |    !inferSbDcSigCoeffFlag ) )       {     sig_coeff_flag[ xC ][ yC ]    }    absLevel[ xC ][ yC ] = 0    if( sig_coeff_flag[ xC ][ yC ] ) {      par_level_flag[ xC ][ yC ]      rem_abs_gt1_flag[ xC ][ yC ] absLevel[ xC ][ yC ] = 1 + par_level_flag[ xC ][ yC ] + 2* rem_abs_gt1_flag[ xC ][ yC ]    }    absLevel1[ xC ][ yC ] = absLevel[ xC ][ yC ]    state = ( stateTransTable >> ( ( state << 2 ) + ( par_level_flag[    xC ][ yC ] << 1 ) ) ) & 3   }   //===== second pass: gt2 =====   for( n = numSbCoeff − 1; n >= 0; n− − ) {    xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ n ][ 1 ]    if( rem_abs_gt1_flag[ xC ][ yC ] ) {     rem_abs_gt2_flag[ xC ][ yC ]     absLevel[ xC ][ yC ] = absLevel[ xC ][ yC ] + 2 *     rem_gt2_flag[ xC ][ yC ]    }   }   //===== third pass: bypass bins of remainder =====   for( n = numSbCoeff − 1; n >= 0; n− − ) {    xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ n ][ 1 ]    if( rem_abs_gt2_flag[ xC ][ yC ] ) {     abs_remainder[ xC ][ yC ]     absLevel[ xC ][ yC ] = absLevel[ xC ][ yC ] + 2 *     abs_remainder[ xC ][ yC ]    }   }   //===== fourth pass: signs =====   for( n = numSbCoeff − 1; n >= 0; n− − ) {    xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ n ][ 1 ]    if( sig_coeff_flag[ xC ][ yC ] ) {     coeff_sign_flag[ xC ][ yC ]     TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] =        absLevel[ xC ][ yC ] * ( 1 − 2 * coeff_sign_flag[ xC        ][ yC ] )    }   }  } }

With respect to Table 4, JVET⁻K0072, provides the following semantics for par_level_flag, rem_abs_gt1_flag, rem_abs_gt2_flag:

par_level_flag[n] specifies the parity of the transform coefficient level at scanning position n. When par_level_flag[n] is not present, it is inferred to be equal to 0.

rem_abs_gt1_flag[n] specifies whether the syntax element rem_abs_gt1_flag[n] is present for the scanning position n. When rem_abs_gt1_flag[n] is not present, it is inferred to be equal to 0.

rem_abs_gt2_flag[n] specifies whether the syntax element abs_remainder[n] is present for the scanning position n. When rem_abs_gt2_flag[n] is not present, it is inferred to be equal to 0.

It should be noted that JVET-K0072 provides where par_level_flag, rem_abs_gt1_flag, and rem_abs_gt2_flag are assigned a context for entorpy coding.

Table 5 provides a summary of possible level values of a coefficient in a sub-block having significant coefficients according to values of sig_coeff_flag, par_level_flag, rem_abs_gt1_flag, rem_abs_gt2_flag, and abs_remainder in JVET-K0072.

TABLE 5 sig_coeff_flag par_level_flag rem_abs_gt1_flag rem_abs_gt2_flag abs_remainder Coefficient Level Value 0 Not Signaled Not Signaled Not Signaled Not Signaled 0 1 0 0 Not Signaled Not Signaled (1 − 2 * coeff_sign_flag) 1 1 0 Not Signaled Not Signaled 2*(1 − 2 * coeff_sign_flag) 1 0 1 0 Not Signaled 3*(1 − 2 * coeff_sign_flag) 1 1 1 0 Not Signaled 4*(1 − 2 * coeff_sign_flag) 1 0 1 1 Signaled (3 + 2 + 2*abs_remainder) *(1 − 2 * coeff_sign_flag) 1 1 1 1 Signaled (4 + 2 + 2*abs_remainder) *(1 − 2 * coeff_sign_flag)

-   -   It should be noted that in ITU-T H.265, in order to limit         decoding complexity, one or more 16-bit cabac_zero_word syntax         elements having a value of 0x0000 are appended to a network         abstraction layer (NAL) unit if a bin-to-bit ratio becomes too         high. That is, in ITU-T H.265, there is a constraint on the         maximum number of bins that may be coded at a particular         bit-rate.

FIG. 3 is a block diagram illustrating an example of a system that may be configured to code (i.e., encode and/or decode) video data according to one or more techniques of this disclosure. System 100 represents an example of a system that may perform video coding using partitioning techniques described according to one or more techniques of this disclosure. As illustrated in FIG. 3 , system 100 includes source device 102, communications medium 110, and destination device 120. In the example illustrated in FIG. 3 , source device 102 may include any device configured to encode video data and transmit encoded video data to communications medium 110. Destination device 120 may include any device configured to receive encoded video data via communications medium 110 and to decode encoded video data. Source device 102 and/or destination device 120 may include computing devices equipped for wired and/or wireless communications and may include set top boxes, digital video recorders, televisions, desktop, laptop, or tablet computers, gaming consoles, mobile devices, including, for example, “smart” phones, cellular telephones, personal gaming devices, and medical imagining devices.

Communications medium 110 may include any combination of wireless and wired communication media, and/or storage devices. Communications medium 110 may include coaxial cables, fiber optic cables, twisted pair cables, wireless transmitters and receivers, routers, switches, repeaters, base stations, or any other equipment that may be useful to facilitate communications between various devices and sites. Communications medium 110 may include one or more networks. For example, communications medium 110 may include a network configured to enable access to the World Wide Web, for example, the Internet. A network may operate according to a combination of one or more telecommunication protocols. Telecommunications protocols may include proprietary aspects and/or may include standardized telecommunication protocols. Examples of standardized telecommunications protocols include Digital Video Broadcasting (DVB) standards, Advanced Television Systems Committee (ATSC) standards, Integrated Services Digital Broadcasting (ISDB) standards, Data Over Cable Service Interface Specification (DOCSIS) standards, Global System Mobile Communications (GSM) standards, code division multiple access (CDMA) standards, 3rd Generation Partnership Project (3GPP) standards, European Telecommunications Standards Institute (ETSI) standards, Internet Protocol (IP) standards, Wireless Application Protocol (WAP) standards, and Institute of Electrical and Electronics Engineers (IEEE) standards.

Storage devices may include any type of device or storage medium capable of storing data. A storage medium may include a tangible or non-transitory computer-readable media. A computer readable medium may include optical discs, flash memory, magnetic memory, or any other suitable digital storage media. In some examples, a memory device or portions thereof may be described as non-volatile memory and in other examples portions of memory devices may be described as volatile memory. Examples of volatile memories may include random access memories (RAM), dynamic random access memories (DRAM), and static random access memories (SRAM). Examples of non-volatile memories may include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. Storage device(s) may include memory cards (e.g., a Secure Digital (SD) memory card), internal/external hard disk drives, and/or internal/external solid state drives. Data may be stored on a storage device according to a defined file format.

Referring again to FIG. 3 , source device 102 includes video source 104, video encoder 106, and interface 108. Video source 104 may include any device configured to capture and/or store video data. For example, video source 104 may include a video camera and a storage device operably coupled thereto. Video encoder 106 may include any device configured to receive video data and generate a compliant bitstream representing the video data. A compliant bitstream may refer to a bitstream that a video decoder can receive and reproduce video data therefrom. Aspects of a compliant bitstream may be defined according to a video coding standard. When generating a compliant bitstream video encoder 106 may compress video data. Compression may be lossy (discernible or indiscernible) or lossless. Interface 108 may include any device configured to receive a compliant video bitstream and transmit and/or store the compliant video bitstream to a communications medium. Interface 108 may include a network interface card, such as an Ethernet card, and may include an optical transceiver, a radio frequency transceiver, or any other type of device that can send and/or receive information. Further, interface 108 may include a computer system interface that may enable a compliant video bitstream to be stored on a storage device. For example, interface 108 may include a chipset supporting Peripheral Component Interconnect (PCI) and Peripheral Component Interconnect Express (PCIe) bus protocols, proprietary bus protocols, Universal Serial Bus (USB) protocols, I²C, or any other logical and physical structure that may be used to interconnect peer devices.

Referring again to FIG. 3 , destination device 120 includes interface 122, video decoder 124, and display 126. Interface 122 may include any device configured to receive a compliant video bitstream from a communications medium. Interface 108 may include a network interface card, such as an Ethernet card, and may include an optical transceiver, a radio frequency transceiver, or any other type of device that can receive and/or send information. Further, interface 122 may include a computer system interface enabling a compliant video bitstream to be retrieved from a storage device. For example, interface 122 may include a chipset supporting PCI and PCIe bus protocols, proprietary bus protocols, USB protocols, I²C, or any other logical and physical structure that may be used to interconnect peer devices. Video decoder 124 may include any device configured to receive a compliant bitstream and/or acceptable variations thereof and reproduce video data therefrom. Display 126 may include any device configured to display video data. Display 126 may comprise one of a variety of display devices such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display. Display 126 may include a High Definition display or an Ultra High Definition display. It should be noted that although in the example illustrated in FIG. 3 , video decoder 124 is described as outputting data to display 126, video decoder 124 may be configured to output video data to various types of devices and/or sub-components thereof. For example, video decoder 124 may be configured to output video data to any communication medium, as described herein.

FIG. 4 is a block diagram illustrating an example of video encoder 200 that may implement the techniques for encoding video data described herein. It should be noted that although example video encoder 200 is illustrated as having distinct functional blocks, such an illustration is for descriptive purposes and does not limit video encoder 200 and/or sub-components thereof to a particular hardware or software architecture. Functions of video encoder 200 may be realized using any combination of hardware, firmware, and/or software implementations. In one example, video encoder 200 may be configured to encode video data according to the techniques described herein. Video encoder 200 may perform intra prediction coding and inter prediction coding of picture areas, and, as such, may be referred to as a hybrid video encoder. In the example illustrated in FIG. 4 , video encoder 200 receives source video blocks. In some examples, source video blocks may include areas of picture that has been divided according to a coding structure. For example, source video data may include macroblocks, CTUs, CBs, sub-divisions thereof, and/or another equivalent coding unit. In some examples, video encoder 200 may be configured to perform additional sub-divisions of source video blocks. It should be noted that some techniques described herein may be generally applicable to video coding, regardless of how source video data is partitioned prior to and/or during encoding. In the example illustrated in FIG. 4 , video encoder 200 includes summer 202, transform coefficient generator 204, coefficient quantization unit 206, inverse quantization/transform processing unit 208, summer 210, intra prediction processing unit 212, inter prediction processing unit 214, filter unit 216, and entropy encoding unit 218.

As illustrated in FIG. 4 , video encoder 200 receives source video blocks and outputs a bitstream. Video encoder 200 may generate residual data by subtracting a predictive video block from a source video block. Summer 202 represents a component configured to perform this subtraction operation. In one example, the subtraction of video blocks occurs in the pixel domain. Transform coefficient generator 204 applies a transform, such as a discrete cosine transform (DCT), a discrete sine transform (DST), or a conceptually similar transform, to the residual block or sub-divisions thereof (e.g., four 8×8 transforms may be applied to a 16×16 array of residual values) to produce a set of residual transform coefficients. Transform coefficient generator 204 may be configured to perform any and all combinations of the transforms included in the family of discrete trigonometric transforms. As described above, in ITU-T H.265, TBs are restricted to the following sizes 4×4, 8×8, 16×16, and 32×32. In one example, transform coefficient generator 204 may be configured to perform transformations according to arrays having sizes of 4×4, 8×8, 16×16, and 32×32. In one example, transform coefficient generator 204 may be further configured to perform transformations according to arrays having other dimensions. In particular, in some cases, it may be useful to perform transformations on rectangular arrays of difference values. In one example, transform coefficient generator 204 may be configured to perform transformations according to the following sizes of arrays: 2×2, 2×4N, 4M×2, and/or 4M×4N. In one example, a 2-dimensional (2D) M×N inverse transform may be implemented as 1-dimensional (1D) M-point inverse transform followed by a 1D N-point inverse transform. In one example, a 2D inverse transform may be implemented as a 1D N-point vertical transform followed by a 1D N-point horizontal transform. In one example, a 2D inverse transform may be implemented as a 1D N-point horizontal transform followed by a 1D N-point vertical transform. Transform coefficient generator 204 may output transform coefficients to coefficient quantization unit 206.

Coefficient quantization unit 206 may be configured to perform quantization of the transform coefficients. As described above, the degree of quantization may be modified by adjusting a quantization parameter. Coefficient quantization unit 206 may be further configured to determine quantization parameters and output QP data (e.g., data used to determine a quantization group size and/or delta QP values) that may be used by a video decoder to reconstruct a quantization parameter to perform inverse quantization during video decoding. It should be noted that in other examples, one or more additional or alternative parameters may be used to determine a level of quantization (e.g., scaling factors). The techniques described herein may be generally applicable to determining a level of quantization for transform coefficients corresponding to a component of video data based on a level of quantization for transform coefficients corresponding another component of video data.

Referring again to FIG. 4 , quantized transform coefficients are output to inverse quantization/transform processing unit 208. Inverse quantization/transform processing unit 208 may be configured to apply an inverse quantization and an inverse transformation to generate reconstructed residual data. As illustrated in FIG. 4 , at summer 210, reconstructed residual data may be added to a predictive video block. In this manner, an encoded video block may be reconstructed and the resulting reconstructed video block may be used to evaluate the encoding quality for a given prediction, transformation, and/or quantization. Video encoder 200 may be configured to perform multiple coding passes (e.g., perform encoding while varying one or more of a prediction, transformation parameters, and quantization parameters). The rate-distortion of a bitstream or other system parameters may be optimized based on evaluation of reconstructed video blocks. Further, reconstructed video blocks may be stored and used as reference for predicting subsequent blocks.

As described above, a video block may be coded using an intra prediction. Intra prediction processing unit 212 may be configured to select an intra prediction mode for a video block to be coded. Intra prediction processing unit 212 may be configured to evaluate a frame and/or an area thereof and determine an intra prediction mode to use to encode a current block. As illustrated in FIG. 4 , intra prediction processing unit 212 outputs intra prediction data (e.g., syntax elements) to entropy encoding unit 218 and transform coefficient generator 204. As described above, a transform performed on residual data may be mode dependent. As described above, possible intra prediction modes may include planar prediction modes, DC prediction modes, and angular prediction modes. Further, in some examples, a prediction for a chroma component may be inferred from an intra prediction for a luma prediction mode. Inter prediction processing unit 214 may be configured to perform inter prediction coding for a current video block. Inter prediction processing unit 214 may be configured to receive source video blocks and calculate a motion vector for PUs of a video block. A motion vector may indicate the displacement of a PU (or similar coding structure) of a video block within a current video frame relative to a predictive block within a reference frame. Inter prediction coding may use one or more reference pictures. Further, motion prediction may be uni-predictive (use one motion vector) or bi-predictive (use two motion vectors). Inter prediction processing unit 214 may be configured to select a predictive block by calculating a pixel difference determined by, for example, sum of absolute difference (SAD), sum of square difference (SSD), or other difference metrics. As described above, a motion vector may be determined and specified according to motion vector prediction. Inter prediction processing unit 214 may be configured to perform motion vector prediction, as described above. Inter prediction processing unit 214 may be configured to generate a predictive block using the motion prediction data. For example, inter prediction processing unit 214 may locate a predictive video block within a frame buffer (not shown in FIG. 4 ). It should be noted that inter prediction processing unit 214 may further be configured to apply one or more interpolation filters to a reconstructed residual block to calculate sub-integer pixel values for use in motion estimation. Inter prediction processing unit 214 may output motion prediction data for a calculated motion vector to entropy encoding unit 218. As illustrated in FIG. 4 , inter prediction processing unit 214 may receive reconstructed video block via filter unit 216. Filter unit 216 may be configured to perform deblocking and/or Sample Adaptive Offset (SAO) filtering. Deblocking refers to the process of smoothing the boundaries of reconstructed video blocks (e.g., make boundaries less perceptible to a viewer). SAO filtering is a non-linear amplitude mapping that may be used to improve reconstruction by adding an offset to reconstructed video data.

Referring again to FIG. 4 , entropy encoding unit 218 receives quantized transform coefficients and predictive syntax data (i.e., intra prediction data, motion prediction data, QP data, etc.). It should be noted that in some examples, coefficient quantization unit 206 may perform a scan of a matrix including quantized transform coefficients before the coefficients are output to entropy encoding unit 218. In other examples, entropy encoding unit 218 may perform a scan. Entropy encoding unit 218 may be configured to perform entropy encoding according to one or more of the techniques described herein. Entropy encoding unit 218 may be configured to output a compliant bitstream, i.e., a bitstream that a video decoder can receive and reproduce video data therefrom.

FIG. 5 is a block diagram illustrating an example of an entropy encoder that may be configured to encode values of syntax elements according to one or more techniques of this disclosure. Entropy encoding unit 300 may include a context adaptive entropy encoding unit, e.g., a CABAC encoder. As illustrated in FIG. 5 , entropy encoder 300 includes binarization unit 302, binary arithmetic encoding unit 304, and context modeling unit 310. Entropy encoding unit 300 may receive one or more syntax elements values and output a compliant bitstream. As described above, binarization includes representing a value of syntax element in to a bin string. Binarization unit 302 may be configured to receive a value for a syntax element and produce a bin string according to one or more binarization techniques. Binarization unit 302 may use, for example, any one or combination of the following techniques to produce a bin string: fixed length coding, unary coding, truncated unary coding, truncated Rice coding, Golomb coding, exponential Golomb coding, and Golomb-Rice coding.

As described above, binary arithmetic encoding codes a series of 0's and 1's based on the principle of recursive interval subdivision. As further described above, the estimated probability of b, being the LPS (or MPS) may be based on a context index. Binary arithmetic encoding unit 304 is configured to receive a bin string from binarization unit 302 and a context index corresponding to a bin from context modeling unit 306, and perform binary arithmetic encoding on the bin string. That is, binary arithmetic encoding unit 304 is configured to write bits to a bitstream according to a renormalization process and further indicate an observed value of a bin such that a context model may be updated. The context models may be defined according to a video coding standard, such as for example, ITU-T H.265. The context models may be stored in a memory. For example, context modeling unit 306 may store a series of indexed tables and/or utilize mapping functions to determine a context model for a particular bin. It should be noted that the functions of binary coding are not limited to particular function blocks and the example of binary arithmetic encoding unit 304 and context modeling unit 306 in the example FIG. 5 should not be construed as limiting.

As described above, in ITU-T H.265, one or more 16-bit cabac_zero_word syntax elements having a value of 0x0000 are appended to a network abstraction layer (NAL) unit if a bin-to-bit ratio becomes too high. It has been observed that when the process in ITU-T H.265 for coding coefficient level values into a bitstream is modified, for example, according to the techniques described in JVET-K0072, the result is an increase in the rate at which cabac_zero_word syntax elements are inserted into the bitstream. This increase is less than ideal.

In one example, according to the techniques herein, the bin-to-bit ratio at which one or more 16-bit cabac_zero_word syntax elements are appended to NAL units may be increased. For example, in ITU-T H.265 the, current constraint is based on the following: max bin rate=4/3bit rate+(raw image bit rate/32)

In one example, the constraint could be modified as follows: max bin rate=3/2 bit rate+raw sample rate

Further, in one example, the constraint could be disabled, such that no 16-bit cabac_zero_word syntax elements are inserted into the bitstream (or other bitstream padding occurs) regardless of the bin-to-bit ratio. In other examples, binarization of syntax elements, including the syntax elements used to code coefficient level values, may be modified and such modifications may be improve coding efficiency when bitstream padding occurs based on a bin-to-bit ratio constraint. However, it should be noted that techniques for coding coefficient level values described herein may be generally useful for video coding, regardless of any constraints based on a bin-to-bit ratio.

In one example, according to the techniques herein, a coefficient level value may be indicated based on the example syntax illustrated in Table 6.

TABLE 6 residual_coding( x0, y0, log2TrafoSizeX, log2TrafoSizeY, cIdx, stateTransTable ) { ... xS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY − log2SbSize ] [ scanIdx ][ lastSubBlock ][ 0 ] yS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY − log2SbSize ] [ scanIdx ][ lastSubBlock ][ 1 ] xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ lastScanPos ][ 0 ] yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ lastScanPos ][ 1 ]  } while( ( xC != LastSignificantCoeffX ) | | ( yC !=  LastSignificantCoeffY ) )  state = 0  for( i = lastSubBlock; i >= 0; i− − ) {   xS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY −   log2SbSize ]        [ scanIdx ][ lastSubBlock ][ 0 ]   yS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY −   log2SbSize ]        [ scanIdx ][ lastSubBlock ][ 1 ]   inferSbDcSigCoeffFlag = 0   if( ( i < lastSubBlock ) && ( i > 0 ) ) {    coded_sub_block_flag[ xS ][ yS ]    inferSbDcSigCoeffFlag = 1   }   for( n = ( i = = lastSubBlock ) ? lastScanPos − 1 : numSbCoeff − 1;   n >= 0; n− − ) {    xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 1 ]    if( coded_sub_block_flag[ xS ][ yS ] && ( n > 0 | |    !inferSbDcSigCoeffFlag ) )        {     sig_coeff_flag[ xC ][ yC ]    }    if( sig_coeff_flag[ xC ][ yC ] ) {     rem_abs_gt1_flag[ n ]     if( rem_abs_gt1_flag[ n ]) {      rem_abs_gt2_flag[ n ]      if( rem_abs_gt2_flag[ n ])       par_level_flag[ n ]     }     if( lastSigScanPosSb = = −1 )      lastSigScanPosSb = n     firstSigScanPosSb = n    }    absLevel[ xC ][ yC ] = sig_coeff_flag[ xC ][ yC ] +    par_level_flag[ n ] +        rem_abs_gt1_flag[ n ] + rem_abs_gt2_flag[ n ]    absLevel1[ xC ][ yC ] = absLevel[ xC ][ yC ]    state = ( stateTransTable >> ( ( state << 2 ) + ( par_level_flag[    xC ][ yC ] << 1 ) ) ) & 3   }   for( n = numSbCoeff − 1; n >= 0; n− − ) {    xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 1 ]    if( rem_abs_gt2_flag[ xC ][ yC ] ) {     abs_remainder[ xC ][ yC ]     absLevel[ xC ][ yC ] = absLevel[ xC ][ yC ] + 2 *     abs_remainder[ xC ][ yC ]    }   }   for( n = numSbCoeff − 1; n >= 0; n− − ) {    xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 1 ]    if( sig_coeff_flag[ xC ][ yC ] ) {     coeff_sign_flag[ xC ][ yC ]     TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] =         absLevel[ xC ][ yC ] * ( 1 − 2 * coeff_sign_flag[         xC ][ yC ] )    }   }  } }

Table 7 provides a summary of possible level values of a coefficient in a sub-block having significant coefficients according to values of sig_coeff_flag, par_level_flag, rem_abs_gt1_flag, rem_abs_gt2_flag, and abs_remainder in Table 6.

TABLE 7 sig_coeff_flag rem_abs_gt1_flag rem_abs_gt2_flag par_level_flag abs_remainder Coefficient Level Value 0 Not Signaled Not Signaled Not Signaled Not Signaled 0 1 0 Not Signaled Not Signaled Not Signaled (1 − 2 * coeff_sign_flag) 1 1 0 Not Signaled Not Signaled 2*(1 − 2 * coeff_sign_flag) 1 1 1 0 Signaled (3 + 2*abs_remainder) *(1 − 2 * coeff_sign_flag) 1 1 1 1 Signaled (4 + 2*abs_remainder) *(1 − 2 * coeff_sign_flag)

It should be noted that when the example syntax illustrated in Table 6 is compared to the syntax illustrated in Table 4, the following may be observed: the worst case number of context coded bins is unchanged; the number of contexts may remain unchanged; there may be fewer bins in the typical case (i.e., value 1 uses fewer bins, 2 vs 3); it may be more efficient because value 1 uses fewer bins (less extreme probabilities); and the syntax utilizes one fewer loop.

In one example, according to the techniques herein, a coefficient level value may be indicated based on the example syntax illustrated in Table 8.

TABLE 8 residual_coding( x0, y0, log2TrafoSizeX, log2TrafoSizeY, cIdx, stateTransTable ) { ... xS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY − log2SbSize ] [ scanIdx ][ lastSubBlock ][ 0 ] yS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY − log2SbSize ] [ scanIdx ][ lastSubBlock ][ 1 ] xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ lastScanPos ][ 0 ] yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ lastScanPos ][ 1 ]  } while( ( xC != LastSignificantCoeffX ) | | ( yC !=  LastSignificantCoeffY ) )  state = 0  for( i = lastSubBlock; i >= 0; i− − ) {   xS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY −   log2SbSize ]        [ scanIdx ][ lastSubBlock ][ 0 ]   yS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY −   log2SbSize ]        [ scanIdx ][ lastSubBlock ][ 1 ]   inferSbDcSigCoeffFlag = 0   if( ( i < lastSubBlock ) && ( i > 0 ) ) {    coded_sub_block_flag[ xS ][ yS ]    inferSbDcSigCoeffFlag = 1   }   for( n = ( i = = lastSubBlock ) ? lastScanPos − 1 : numSbCoeff − 1;   n >= 0; n− − ) {    xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 1 ]    if( coded_sub_block_flag[ xS ][ yS ] && ( n > 0 | |    !inferSbDcSigCoeffFlag ) ) {     sig_coeff_flag[ xC ][ yC ]    }    if( sig_coeff_flag[ xC ][ yC ] ) {     rem_abs_gt1_flag[ n ]     if( rem_abs_gt1_flag[ n ]) {      rem_abs_gt2_flag[ n ]      if( rem_abs_gt2_flag[ n ])       par_level_flag[ n ]       rem_abs_gt3_flag[ n ]     }     if( lastSigScanPosSb = = −1 )      lastSigScanPosSb = n     firstSigScanPosSb = n    }    absLevel[ xC ][ yC ] = sig_coeff_flag[ xC ][ yC ] +    par_level_flag[ n ] +        rem_abs_gt1_flag[ n ] + rem_abs_gt2_flag[ n ] +        2 * rem_abs_gt3_flag[ n ]    absLevel1[ xC ][ yC ] = absLevel[ xC ][ yC ]    state = ( stateTransTable >> ( ( state << 2 ) + ( par_level_flag[    xC ][ yC ] << 1 ) ) ) & 3   }   for( n = numSbCoeff − 1; n >= 0; n− − ) {    xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 1 ]    if( rem_abs_gt3_flag[ xC ][ yC ] ) {     abs_remainder[ xC ][ yC ]     absLevel[ xC ][ yC ] = absLevel[ xC ][ yC ] + 2 *     abs_remainder[ xC ][ yC ]    }   }   for( n = numSbCoeff − 1; n >= 0; n− − ) {    xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 1 ]    if( sig_coeff_flag[ xC ][ yC ] ) {     coeff_sign_flag[ xC ][ yC ]     TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] =         absLevel[ xC ][ yC ] * ( 1 − 2 * coeff_sign_flag[ xC         ][ yC ] )    }   }  } }

Table 9 provides a summary of possible level values of a coefficient in a sub-block having significant coefficients according to values of sig_coeff_flag, par_level_flag, rem_abs_gt1_flag, rem_abs_gt2_flag, rem_abs_gt3_flag and abs_remainder in Table 8.

TABLE 9 sig_coeff_flag rem_abs_gt1_flag rem_abs_gt2_flag par_level_flag rem_abs_gt3_flag abs_remainder Coefficient Level Value 0 Not Signaled Not Signaled Not Signaled Not Signaled Not Signaled 0 1 0 Not Signaled Not Signaled Not Signaled Not Signaled (1 − 2 * coeff_sign_flag) 1 1 0 Not Signaled Not Signaled Not Signaled 2*(1 − 2 * coeff_sign_flag) 1 1 1 0 0 Signaled (4 + 2*abs_remainder) *(1 − 2 * coeff_sign_flag) 1 1 1 0 1 Signaled (6 + 2*abs_remainder) *(1 − 2 * coeff_sign_flag) 1 1 1 1 0 Signaled (3 + 2*abs_remainder) *(1 − 2 * coeff_sign_flag) 1 1 1 1 1 Signaled (5 + 2*abs_remainder) *(1 − 2 * coeff_sign_flag)

It should be noted that when the example syntax illustrated in Table 7 is compared to the syntax illustrated in Table 4, the following may be observed: there may be fewer bins in the typical case (i.e., value 1 uses fewer bins); it may be more efficient because value 1 uses fewer bins (less extreme probabilities); and the syntax utilizes one fewer loop.

In one example, according to the techniques herein, a coefficient level value may be indicated based on the example syntax illustrated in Table 10.

TABLE 10 residual_coding( x0, y0, log2TrafoSizeX, log2TrafoSizeY, cIdx, stateTransTable ) { ... xS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY − log2SbSize ] [ scanIdx ][ lastSubBlock ][ 0 ] yS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY − log2SbSize ] [ scanIdx ][ lastSubBlock ][ 1 ] xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ lastScanPos ][ 0 ] yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ lastScanPos ][ 1 ]  } while( ( xC != LastSignificantCoeffX ) | | ( yC !=  LastSignificantCoeffY ) )  state = 0  for( i = lastSubBlock; i >= 0; i− − ) {   xS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY −   log2SbSize ]       [ scanIdx ][ lastSubBlock ][ 0 ]   yS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY −   log2SbSize ]       [ scanIdx ][ lastSubBlock ][ 1 ]   inferSbDcSigCoeffFlag = 0   if( ( i < lastSubBlock ) && ( i > 0 ) ) {    coded_sub_block_flag[ xS ][ yS ]    inferSbDcSigCoeffFlag = 1   }   for( n = ( i = = lastSubBlock ) ? lastScanPos − 1 : numSbCoeff − 1;   n >= 0; n− − ) {    xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 1 ]    if( coded_sub_block_flag[ xS ][ yS ] )     par_level_flag[ n ]    if( coded_sub_block_flag[ xS ][ yS ] && ( n > 0 | |    !inferSbDcSigCoeffFlag ||       par_level_flag[ n ] ) ) {     sig_coeff_flag[ xC ][ yC ]    }    if( sig_coeff_flag[ xC ][ yC ] )     rem_abs_gt1_flag[ n ]    absLevel[ xC ][ yC ] = 2 * sig_coeff_flag[ xC ][ yC ] +    par_level_flag[ n ] + 2 *       rem_abs_gt1_flag[ n ]    if( absLevel [ xC ][ yC ] ) {     if( lastSigScanPosSb = = −1 )      lastSigScanPosSb = n     firstSigScanPosSb = n    }    absLevel1[ xC ][ yC ] = absLevel[ xC ][ yC ]    state = ( stateTransTable >> ( ( state << 2 ) + ( !par_level_flag[    xC ][ yC ] << 1 ) ) ) & 3   }   for( n = numSbCoeff − 1; n >= 0; n− − ) {    xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 1 ]    if( rem_abs_gt1_flag[ xC ][ yC ] ) {     abs_remainder[ xC ][ yC ]     absLevel[ xC ][ yC ] = absLevel[ xC ][ yC ] + 2 *     abs_remainder[ xC ][ yC ]    }   }   for( n = numSbCoeff − 1; n >= 0; n− − ) {    xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 1 ]    if( absLevel1[ xC ][ yC ] ) {     coeff_sign_flag[ xC ][ yC ]     TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] =        absLevel[ xC ][ yC ] * ( 1 − 2 * coeff_sign_flag[ xC ][        yC ] )    }   }  } }

Table 11 provides a summary of possible level values of a coefficient in a sub-block having significant coefficients according to values of sig_coeff_flag, par_level_flag, rem_abs_gt1_flag, and abs_remainder in Table 10.

TABLE 11 par_level_flag sig_coeff_flag rem_abs_gt1_flag abs_remainder Coefficient Level Value 0 0 Not Signaled Not Signaled 0 1 0 Not Signaled Not Signaled (1 − 2 * coeff_sign_flag) 0 1 0 Not Signaled 2*(1 − 2 * coeff_sign_flag) 0 1 1 Signaled (4 + 2*abs_remainder) *(1 − 2 * coeff_sign_flag) 1 1 0 Not Signaled 3*(1 − 2 * coeff_sign_flag) 1 1 1 Signaled (5 + 2*abs_remainder) *(1 − 2 * coeff_sign_flag)

It should be noted that when the example syntax illustrated in Table 10 is compared to the syntax illustrated in Table 4, the following may be observed, the worst case number of context coded bins is reduced and the number of contexts may be reduced.

In one example, according to the techniques herein, a coefficient level value may be indicated based on the example syntax illustrated in Table 12.

TABLE 12 residual_coding( x0, y0, log2TrafoSizeX, log2TrafoSizeY, cIdx, stateTransTable ) { ... xS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY − log2SbSize ] [ scanIdx ][ lastSubBlock ][ 0 ] yS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY − log2SbSize ] [ scanIdx ][ lastSubBlock ][ 1 ] xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ lastScanPos ][ 0 ] yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize ][ scanIdx ][ lastScanPos ][ 1 ]  } while( ( xC != LastSignificantCoeffX ) | | ( yC !=  LastSignificantCoeffY ) )  state = 0  for( i = lastSubBlock; i >= 0; i− − ) {   xS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY −   log2SbSize ]       [ scanIdx ][ lastSubBlock ][ 0 ]   yS = ScanOrder[ log2TrafoSizeX − log2SbSize ][ log2TrafoSizeY −   log2SbSize ]       [ scanIdx ][ lastSubBlock ][ 1 ]   inferSbDcSigCoeffFlag = 0   if( ( i < lastSubBlock ) && ( i > 0 ) ) {    coded_sub_block_flag[ xS ][ yS ]    inferSbDcSigCoeffFlag = 1   }   for( n = ( i = = lastSubBlock ) ? lastScanPos − 1 : numSbCoeff − 1;   n >= 0; n− − ) {    xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 1 ]    if( coded_sub_block_flag[ xS ][ yS ] && ( n > 0 | |    !inferSbDcSigCoeffFlag ) ) {     sig_coeff_flag[ xC ][ yC ]    }    if( sig_coeff_flag[ xC ][ yC ] ) {     rem_abs_gt1_flag[ n ]     if( rem_abs_gt1_flag[ n ]) {      par_level_flag[ n ]      rem_abs_gt2_flag[ n ] // Note: order of par_level_flag and rem_abs_gt2_flag could be switched     }     if( lastSigScanPosSb = = −1 )      lastSigScanPosSb = n     firstSigScanPosSb = n    }    absLevel[ xC ][ yC ] = sig_coeff_flag[ xC ][ yC ] −    par_level_flag[ n ] + 2 *       rem_abs_gt1_flag[ n ] + 2 * rem_abs_gt2_flag[ n ]    absLevel1[ xC ][ yC ] = absLevel[ xC ][ yC ]    state = ( stateTransTable >> ( ( state << 2 ) + ( par_level_flag[    xC ][ yC ] << 1 ) ) ) & 3   }   for( n = numSbCoeff − 1; n >= 0; n− − ) {    xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 1 ]    if( rem_abs_gt2_flag[ xC ][ yC ] ) {     abs_remainder[ xC ][ yC ]     absLevel[ xC ][ yC ] = absLevel[ xC ][ yC ] + 2 *     abs_remainder[ xC ][ yC ]    }   }   for( n = numSbCoeff − 1; n >= 0; n− − ) {    xC = ( xS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 0 ]    yC = ( yS << log2SbSize ) + ScanOrder[ log2SbSize ][ log2SbSize    ][ scanIdx ][ n ][ 1 ]    if( sig_coeff_flag[ xC ][ yC ] ) {     coeff_sign_flag[ xC ][ yC ]     TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] =        absLevel[ xC ][ yC ] * ( 1 − 2 * coeff_sign_flag[ xC ][        yC ] )    }   }  } }

Table 13 provides a summary of possible level values of a coefficient in a sub-block having significant coefficients according to values of sig_coeff_flag, par_level_flag, rem_abs_gt1_flag, rem_abs_gt2_flag, and abs remainder in Table 12.

TABLE 13 sig_coeff_flag rem_abs_gt1_flag rem_abs_gt2_flag par_level_flag abs_remainder Coefficient Level Value 0 Not Signaled Not Signaled Not Signaled Not Signaled 0 1 0 Not Signaled Not Signaled Not Signaled (1 − 2 * coeff_sign_flag) 1 1 0 1 Not Signaled 2*(1 − 2 * coeff_sign_flag) 1 1 0 0 Not Signaled 3*(1 − 2 * coeff_sign_flag) 1 1 1 1 Signaled (4 + 2*abs_remainder) *(1 − 2 * coeff_sign_flag) 1 1 1 0 Signaled (5 + 2*abs_remainder) *(1 − 2 * coeff_sign_flag)

It should be noted that when the example syntax illustrated in Table 12 is compared to the syntax illustrated in Table 4, the following may be observed, the worst case number of context coded bins is unchanged; the number of contexts may remain unchanged; there may be fewer bins in the typical case (i.e., value 1 uses fewer bins (2 vs. 3)); it may be more efficient because value 1 uses fewer bins (less extreme probabilities); and the syntax utilizes one fewer loop.

In this manner, video encoder represents an example of a device configured to determine whether a coefficient level value is equal to one, and in the case where the coefficient level value is equal to one indicate that the coefficient level value is equal to one by signaling values for a first flag and a second flag, in the case where the coefficient level value is greater than one determine whether the coefficient level value is greater than or equal to three, in the case where the coefficient level value is not greater than or equal to three, indicate that the coefficient level value is equal to two by signaling values for the first flag, the second flag, and a third flag, in the case where the coefficient level value is greater than or equal to three, indicate a value of the coefficient level by signaling values for the first flag, the second flag, the third flag, and a fourth flag.

FIG. 6 is a block diagram illustrating an example of a video decoder that may be configured to decode video data according to one or more techniques of this disclosure. In one example, video decoder 400 may be configured to reconstruct video data based on one or more of the techniques described above. That is, video decoder 400 may operate in a reciprocal manner to video encoder 200 described above. Video decoder 400 may be configured to perform intra prediction decoding and inter prediction decoding and, as such, may be referred to as a hybrid decoder. In the example illustrated in FIG. 6 video decoder 400 includes an entropy decoding unit 402, inverse quantization unit 404, inverse transformation processing unit 406, intra prediction processing unit 408, inter prediction processing unit 410, summer 412, filter unit 414, and reference buffer 416. Video decoder 400 may be configured to decode video data in a manner consistent with a video encoding system, which may implement one or more aspects of a video coding standard. It should be noted that although example video decoder 400 is illustrated as having distinct functional blocks, such an illustration is for descriptive purposes and does not limit video decoder 400 and/or sub-components thereof to a particular hardware or software architecture. Functions of video decoder 400 may be realized using any combination of hardware, firmware, and/or software implementations.

As illustrated in FIG. 6 , entropy decoding unit 402 receives an entropy encoded bitstream. Entropy decoding unit 402 may be configured to decode quantized syntax elements and quantized coefficients from the bitstream according to a process reciprocal to an entropy encoding process. Entropy decoding unit 402 may be configured to perform entropy decoding according any of the entropy coding techniques described above. Entropy decoding unit 402 may parse an encoded bitstream in a manner consistent with a video coding standard. Video decoder 400 may be configured to parse an encoded bitstream where the encoded bitstream is generated based on the techniques described above.

FIG. 7 is a block diagram illustrating an example entropy decoding unit that may implement one or more of the techniques described in this disclosure. Entropy decoding unit 500 receives an entropy encoded bitstream and decodes syntax elements from the bitstream. As illustrated in FIG. 7 , entropy decoding unit 500 includes a binary arithmetic decoding module 502, a context modeling unit 504 and a binarization unit 506. Entropy decoding unit 500 may perform reciprocal functions to entropy encoding unit 300 described above with respect to FIG. 5 .

As shown in FIG. 7 , context modeling unit 508 and a binarization unit 506 receive a request for a syntax element value. Context modeling unit 504 determines a context index for the syntax element. Further, context modeling unit 504 updates a context index based on the determination made by binary arithmetic decoding module 502, for example, according to the probability estimate techniques described above. Binary arithmetic decoding module 502 receives n bits from the bitstream, i.e., the arithmetic code, and outputs a sequence of parsed bins based on the arithmetic code and the calculated sub-intervals. Binarization unit 506 determines possible valid binarization values for a syntax element and uses a bin matching function to determine if a series parsed bin values corresponds to a valid value for the syntax element. When a series bin values corresponds to a valid value for the syntax element, the value of the syntax element is output. That is, entropy decoding unit 500 is configured to determine the value of a bin based on the current sub-interval and bits from the bitstream, based on techniques described herein. In this manner, video decoder 400 represents an example of a device configured to parse a first and second flag included in a bitstream, determine that a coefficient level value is greater than one based on the values of the parsed first and second flags, parse a third and fourth flag included in the bitstream, determine whether the coefficient level value is an odd number greater than or equal to three or an even number greater than or equal to four based on the values of the parsed third and fourth flag.

Referring again to FIG. 6 , inverse quantization unit 404 receives quantized transform coefficients (i.e., level values) and quantization parameter data from entropy decoding unit 402. Quantization parameter data may include any and all combinations of delta QP values and/or quantization group size values and the like described above. Video decoder 400 and/or inverse quantization unit 404 may be configured to determine QP values used for inverse quantization based on values signaled by a video encoder and/or through video properties and/or coding parameters. That is, inverse quantization unit 404 may operate in a reciprocal manner to coefficient quantization unit 206 described above. For example, inverse quantization unit 404 may be configured to infer predetermined values), allowed quantization group sizes, and the like, according to the techniques described above. Inverse quantization unit 404 may be configured to apply an inverse quantization. Inverse transform processing unit 406 may be configured to perform an inverse transformation to generate reconstructed residual data. The techniques respectively performed by inverse quantization unit 404 and inverse transform processing unit 406 may be similar to techniques performed by inverse quantization/transform processing unit 208 described above. Inverse transform processing unit 406 may be configured to apply an inverse DCT, an inverse DST, an inverse integer transform, Non-Separable Secondary Transform (NSST), or a conceptually similar inverse transform processes to the transform coefficients in order to produce residual blocks in the pixel domain. Further, as described above, whether a particular transform (or type of particular transform) is performed may be dependent on an intra prediction mode. As illustrated in FIG. 6 , reconstructed residual data may be provided to summer 412. Summer 412 may add reconstructed residual data to a predictive video block and generate reconstructed video data. A predictive video block may be determined according to a predictive video technique (i.e., intra prediction and inter frame prediction).

Intra prediction processing unit 408 may be configured to receive intra prediction syntax elements and retrieve a predictive video block from reference buffer 416. Reference buffer 416 may include a memory device configured to store one or more frames of video data. Intra prediction syntax elements may identify an intra prediction mode, such as the intra prediction modes described above. In one example, intra prediction processing unit 308 may reconstruct a video block using according to one or more of the intra prediction coding techniques described herein. Inter prediction processing unit 410 may receive inter prediction syntax elements and generate motion vectors to identify a prediction block in one or more reference frames stored in reference buffer 416. Inter prediction processing unit 410 may produce motion compensated blocks, possibly performing interpolation based on interpolation filters. Identifiers for interpolation filters to be used for motion estimation with sub-pixel precision may be included in the syntax elements. Inter prediction processing unit 410 may use interpolation filters to calculate interpolated values for sub-integer pixels of a reference block. Filter unit 414 may be configured to perform filtering on reconstructed video data. For example, filter unit 414 may be configured to perform deblocking and/or SAO filtering, as described above with respect to filter unit 216. Further, it should be noted that in some examples, filter unit 414 may be configured to perform proprietary discretionary filter (e.g., visual enhancements). As illustrated in FIG. 6 , a reconstructed video block may be output by video decoder 400.

In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

Moreover, each functional block or various features of the base station device and the terminal device used in each of the aforementioned embodiments may be implemented or executed by a circuitry, which is typically an integrated circuit or a plurality of integrated circuits. The circuitry designed to execute the functions described in the present specification may comprise a general-purpose processor, a digital signal processor (DSP), an application specific or general application integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic devices, discrete gates or transistor logic, or a discrete hardware component, or a combination thereof. The general-purpose processor may be a microprocessor, or alternatively, the processor may be a conventional processor, a controller, a microcontroller or a state machine. The general-purpose processor or each circuit described above may be configured by a digital circuit or may be configured by an analogue circuit. Further, when a technology of making into an integrated circuit superseding integrated circuits at the present time appears due to advancement of a semiconductor technology, the integrated circuit by this technology is also able to be used.

Various examples have been described. These and other examples are within the scope of the following claims. 

The invention claimed is:
 1. A decoder for decoding encoded data, the decoder comprising: a decoding circuitry that, during a first pass, for at least one of subblock scanning positions, decodes: (i) a significant coefficient flag specifying whether a transform coefficient level is non-zero, (ii) a first absolute level greater flag specifying whether a parity level flag is present for a scanning position, in a case that a value of the significant coefficient flag is equal to one, (iii) the parity level flag specifying a parity of the transform coefficient level at the scanning position, in a case that a value of the first absolute level greater flag is equal to one, and (iv) a second absolute level greater flag specifying whether an absolute remainder syntax element is present for the scanning position, in the case that a value of the first absolute level great flag is equal to one, wherein the decoding circuity, during the first pass, derives a first absolute level value for the transform coefficient level based on a sum of (a) the value of the significant coefficient flag, (b) a value of the parity level flag, (c) the value of the first absolute level greater flag, and (d) a product of two and a value of the second absolute value level greater flag, wherein the decoding circuitry, during a second pass, for at least one of the subblock scanning positions, decodes the absolute remainder syntax element specifying a remaining absolute value of the transform coefficient level, in a case that the value of the second absolute level greater flag is equal to one, and the decoding circuitry, during the second pass, derives a second absolute level value for the transform coefficient level by adding the first absolute level value to a product of two and a value of the absolute remainder syntax element.
 2. A method of decoding encoded data, the method including: during a first pass, for at least one of subblock scanning positions: decoding a significant coefficient flag specifying whether a transform coefficient level is non-zero; decoding a first absolute level greater flag specifying whether a parity level flag is present for a scanning position, in a case that a value of the significant coefficient flag is equal to one; decoding the parity level flag specifying a parity of the transform coefficient level at the scanning position, in a case that a value of the first absolute level greater flag is equal to one; decoding a second absolute level greater flag specifying whether an absolute remainder syntax element is present for the scanning position, in the case that the value of the first absolute level greater flag is equal to one; and deriving a first absolute level value for the transform coefficient level based on a sum of (a) the value of the significant coefficient flag, (b) a value of the parity level flag, (c) the value of the first absolute level greater flag, and (d) a product of two and a value of the second absolute value level greater flag; and during a second pass, for at least one of the number of subblock scanning positions: decoding the absolute remainder syntax element specifying a remaining absolute value of the transform coefficient level, in a case that the value of the second absolute level greater flag is equal to one; and deriving a second absolute level value for the transform coefficient level by adding the first absolute level value to a product of two and a value of the absolute remainder syntax element.
 3. An encoder for encoding image data, the encoder comprising: an encoding circuitry that, during a first pass, for at least one of subblock scanning positions, encodes: (i) a significant coefficient flag specifying whether a transform coefficient level is non-zero, (ii) a first absolute level greater flag specifying whether a parity level flag is present for a scanning position, in a case that a value of the significant coefficient flag is equal to one, (iii) the parity level flag specifying a parity of the transform coefficient level at the scanning position, in a case that a value of the first absolute level greater flag is equal to one, and (iv) a second absolute level greater flag specifying whether an absolute remainder syntax element is present for the scanning position, in the case that the value of the first absolute level great flag is equal to one, wherein the encoding circuitry, during the first pass, derives a first absolute level value for the transform coefficient level based on a sum of (a) the value of the significant coefficient flag, (b) a value of the parity level flag, (c) the value of the first absolute level greater flag, and (d) a product of two and a value of the second absolute value level greater flag, wherein the encoding circuitry, during a second pass, for at least one of the subblock scanning positions, encodes the absolute remainder syntax element specifying a remaining absolute value of the transform coefficient level, in a case that the value of the second absolute level greater flag is equal to one, and the encoding circuitry, during the second pass, derives a second absolute level value for the transform coefficient level by adding the first absolute level value to a product of two and a value of the absolute remainder syntax element. 